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The pure air is above the fire, and its place extends
as far as heaven. In this air there is
no darkness. For it was made of pure purity and
it shines and glitters so clearly that nothing
can be compared to it. In this air there are seven stars,
which make their way around the earth. These stars
are very clean and clear and are called the seven
planets, situated one above another. They are ordered
in such a fashion there is more space from one to the next
than the distance from the earth to the moon, a distance that is fifteen times
longer than the size of the earth. Each of the planets
runs its course in the firmament by a miracle, its circle
being larger or smaller depending on how high or low it is.
For the orbits of those closest to the earth are smaller
and quicker to complete than those that are further away.
To explain this in a way that you can understand, one could
make a hole in a wall and draw several circles with a compass
around this point, each of them larger than the one before.
The one that is closes to the hole would be the least of
the others and its circle would be the smallest.